1. Field of the Invention
Films made from natural products are of increasing scientific and commercial interest. These films are not only biodegradable but may also be recyclable as well as acceptable for pharmaceutical applications. Multiple uses, ease of disposal and the replacement of petroleum-based raw materials with renewable agricultural products make these types of films excellent candidates for commercial development.
This invention relates to novel films fabricated from mixtures of pectin and poly(vinyl alcohol) (PVOH). Plasticizers may also be included in the mixtures in order to increase film flexibility. The films are high modulus, flexible and self-supporting and are advantageous in that an agricultural waste product, i.e. pectin, is utilized.
2. Description of the Prior Art
The film-forming properties of several water soluble polysaccharides have been studied. Films useful for coatings made from alginates and carrageenans were disclosed by Kester et al. Food Technology, vol. 12 (1), pp. 47-59, (1986). Paper coatings and similar applications of carboxylmethyl cellulose and other cellulose ethers have been investigated, and studies of chitin and chitosan films, including self-supporting films, have also been carried out (Averback, Proceedings First International Conference, pp. 199-209, 1979; Hosokawa et al., Ind. Eng. Chem. Res., vol. 29, pp. 309-324, 1990; Wong et al., UJNR Protein Panel, 19th Meeting, San Diego, Calif., 1990).
A few studies were carried out on pectin films in the 1930's and 1940's (Henglein et al., Chemisch Berichte, vol. 69(B), pp. 309-324, 1936; Henglein et al., German Patent No. 0680396, 1939; Maclay et al., Chemurugic Digest, vol. 6 (22), pp. 326 -329, 1947; Schultz J. Colloid Sci., vol. 3, pp. 53-62, et al., 1948; Schultz et al., J. of Physical and Colloid Chem., vol. 53, pp. 1320-1330, 1949); however, these studies generally involved derivatized pectins used with divalent cations such as calcium. A more recent work discussed blends of pectins and carboxymethyl cellulose for use as cigarette papers (Hind et al., U.S. Pat. No. 4,129,134, 1978). U.S. Pat. No. 2,542,052 (issued to H.S. Owens and T.H. Schultz) describes films made from low methoxyl (less than 7.4% methoxyl) pectin cross-linked with polyvalent cations. No other polymeric component was used.
Poly(vinyl alcohol) has previously been reported as useful in formulations for producing films or matrices for the delivery of medicaments, such as to a wound site (Sharik, U.S. Pat. No. 5,206,026 issued Apr. 27, 1993) or to the eye (Michaels, U.S. Pat. No. 3,962,414 issued Jun. 8, 1976). PVOH, however, suffers from the disadvantage that it is not readily biodegradable.
Thus, although various types of films may be formed from a variety of film-forming substances, none exhibit the advantageous properties of high modulus, flexibility and biodegradability as do the novel films of the invention described herein.